In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 100 megabits per second (Mbps) for high mobility communication (such as from trains and cars) and 1 gigabit per second (Gbps) for low mobility communication (such as pedestrians and stationary users). Mobile WiMAX Release 2 (also known as WirelessMAN-Advanced or IEEE 802.16m’) and LTE Advanced (LTE-A) are IMT-Advanced compliant backwards compatible versions of the above two systems, standardized during the spring 2011 and promising speeds in the order of 1 Gbps. Computer Networks R. Wei 18
As opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but all-Internet Protocol (IP) based communication such as IP telephony. The spread spectrum radio technology used in 3G systems, is abandoned in all 4G candidate systems and replaced by OFDMA multi-carrier transmission and other frequency-domain equalization (FDE) schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation (echoes). The peak bit rate is further improved by smart antenna arrays for multiple-input multiple-output (MIMO) communications. Computer Networks R. Wei 19
LTE has two important innovations over 3G systems. • Evolved Packet Core (EPC): This is a simplified all-IP core network that unifies the separate circuit-switched cellular voice network and the packet-switched cellular data network. The EPC allows multiple types of radio access networks, including legacy 2G and 3G radio access networks, to attach to the core network. Computer Networks R. Wei 20
• LTE Radio Access Network: LTE uses a combination of frequency division multiplexing and time division multiplexing on the downstream channel, know as orthogonal frequency division multiplexing (OFDM). In LTE, each active mobile node is allocated one or more 0.5 ms time slots in one or more of the channel frequencies. By being allocated increasingly more time slots, a mobile node is able to achieve increasingly higher transmission rates. Slot reallocation among nodes can be performed as often as once every millisecond. Another inovation in the LTE radio network is the use of multiple-input, multiple-output (MIMO) antennas. Computer Networks R. Wei 21
WiMAX refers to interoperable implementations of the IEEE 802.16 family of wireless-networks standards ratified by the WiMAX Forum. The original IEEE 802.16 standard (now called ”Fixed WiMAX”) was published in 2001. WiMAX adopted some of its technology from WiBro, a service marketed in Korea. The term fixed arises because the technology does not provide for handoff among access points. Mobile WiMAX (originally based on 802.16e-2005) is the revision that was deployed in many countries, and is the basis for future revisions such as 802.16m-2011. The technology of the Mobile WiMAX offers handoff among access points, which means the system can be used with portable devices such as laptop computers and cell phones. Computer Networks R. Wei 22
Some key features of WiMAX can briefly summarized as follows: • Uses licensed spectrum (i.e., offed by carriers). • Each cell can cover a radius of 3 to 10 km. • Uses scalable orthogonal FDM. • Guarantees quality of services (for voice or vidio). • Can transport 70 Mbps in each direction at short distances. • Provides 10 Mbps over a long distance (10 km) Computer Networks R. Wei 23
5.2 Wireless LANs: WiFi Although many technologies and standards for wireless LAN were developed, the most common and important standard is the IEEE 802.11 wireless LAN, also known as WiFi. There are several 802.11 standards for wireless LAN technologies, including 802.11.b, 802.11.a and 802.11.g. The main characteristics of these standards are as follows: Standard Frequency Range (United States) Data Rates 802.11a 5.1-5.8 GHz up to 54 Mbps 802.11b 2.4-2.485 GHz up to 11Mbnps 802.11g 2.4-2.485 GHz up to 54 Mbps Computer Networks R. Wei 24
A number of dual-mode (802.11a/b) and tri-mode (802.11a/b/g) devices are also available. The three standards share many characteristics. Some of these characteristics are: • They all use the same medium access protocol CSMA/CA. • They all use the same frame structure for their link-layer frames. • They have the ability to reduce their transmission rate in order to reach out over greater distances. • All of them allow for both “infrastructure mode” and “ad hoc” mode. Computer Networks R. Wei 25
The 802.11b and 802.11g wireless LANs operate in the unlicensed frequency band of 2.4 - 2.485 GHz, competing for frequency spectrum with 2.4 GHz phones and microwave ovens. 802.11a wireless LANs can run at significantly higher rates, but do so at higher frequencies. Due to the higher frequency, 802.11a LANs have a shorter transmission distance for a given power level and suffer more from multipath propagation. A relatively new WiFi standard 802.11n uses multiple input multiple output (MIMO) antennas that are transmitting/receiving different signals. Depending on the modulation scheme used, transmission rates of several hundred megabits per second are possible with 802.11n. Computer Networks R. Wei 26
The 802.11 architecture The basic building block of the 802.11 architecture is the basic service set (BSS). A BSS contains one or more wireless stations and a central base station, know as an access point (AP). The AP in each BSS connects to an interconnection device such as a router, which in turn leads to the Internet. In a typical home network, there is one AP and one router (typically integrated together as on unit) that connects the BSS to the Internet. Each 802.11 wireless station has a 6-bite MAC address that is stored in the firmware of the station’s adapter (network interface card). Each AP also has a MAC address for its wireless interface. As with Ethernet, there MAC addresses are administered by IEEE and are globally unique. Computer Networks R. Wei 27
Wireless LANs that deploy APs are often refereed to as infrastructure wireless LANs, with the infrastructure being the APs along with the wired Ethernet infrastructure that interconnects the APs and a router. IEEE 802.11 stations can also group themselves together to form an ad hoc network, a network with no central control and with no connections to the “out side” world. Computer Networks R. Wei 28
Channels and association In 802.11, each wireless station needs to associate with an AP before it can send or receive network layer data. When a network administrator installs an AP, the administrator assigns a one or two-word Service Set Identifier (SSID) to the access point. The administrator must also assign a channel number to the AP. Computer Networks R. Wei 29
Recall that 802.11 operates in the frequency range of 2.4-2.485 GHz. Within this 85 MHz band, 802.11 defines 11 partially overlapping channels. Any two channels are non-overlapping if an only i they are separated by four or more channels. In particular, the set of channels 1, 6 and 11 is the only set of three non-overlapping channels. This means that an administrator could create a wireless LAN with an aggregate maximum transmission rate of 33 Mbps by installing three 802.11b APs at the same physical location, assigning channels 1, 6, and 11 to APs, and interconnecting each of the APs with a switch. Computer Networks R. Wei 30
The 802.11 standard requires that an AP periodically send beacon frames, , each of which includes the AP’s SSID and MAC address. The wireless station (laptop computer, for example), knowing that AP’s are sending out beacon frames, scans the 11 channels, seeking beacon frames from any AP’s that may be out there. Having learned about available AP’s from the beacon frames, the wireless station selects one of the AP’s for association. Computer Networks R. Wei 31
The process of scanning channels and listening for beacon frames is known as passive scanning. A wireless host can also perform active scanning, by broadcasting a probe frame that will be received by all APs within the wireless host’s range. APs respond to the probe request frame with a probe response frame. The wireless host can then choose the AP with which to associate from among the responding APs. Computer Networks R. Wei 32
After selecting the AP with which to associate, the wireless host sends an association request frame to the AP, and the AP responds with an association response frame. Once associated with an AP, the host will want to join the subnet to which the AP belongs. Thus the host will typically send a DHCP discovery message into the subnet via the AP in order to obtain an IP address on the subnet. Once the address is obtained, the rest of the Internet views that host simply as another host with an IP address in that subnet. Computer Networks R. Wei 33
In order to create an association with a particular AP, the wireless station may be required to authenticate itself to the AP. 802.11 wireless LANs provide several alternatives for authentication and access. One approach, used by many companies, is to permit access to a wireless network based on a station’s MAC address. A second approach, employs usernames and passwords. In both cases, the AP communicates with an authentication server, relaying information between the wireless end-point station and the authentication server using a protocol such as RADIUS (RFC 2865) or DIAMETER (RFC 3588). Separating the authentication server from the AP allows one authentication server to serve many APs, centralizing the decisions of authentication and access within the single server, and keeping AP costs and complexity low. Computer Networks R. Wei 34
The 802.11 MAC protocol Once a wireless station is associated with an AP, it can start sending and receiving data frames to and from the access point. Since multiple stations may want to transmit data frames at the same time over the same channel, some multiple access protocol is needed to coordinate the transmissions. The designers of 802.11 chose a random access protocol for 802.11 wireless LANs. This access protocol is referred to as CSMA with collision avoidance, or CSMA/CA. Computer Networks R. Wei 35
CSMA stands for “carrier sense multiple access”, meaning that each station senses the channel before transmitting, and refrains from transmitting when the channel is sensed busy. Instead of using collision detection (CSMA/CD) in Ethernet, 802.11 uses collision-avoidance technique. Because of the relatively high bit error rates of wireless channels, 802.11 uses a link-layer acknowledgment/retransissin (ARQ) scheme. Computer Networks R. Wei 36
The link-layer acknowledgment scheme is as follows. When a station in a wireless LAN sends a frame, the frame may not reach the destination station intact a variety of reasons. To deal with this problem, the 802.11 MAC protocol applies link-layer acknowledgments. When the destination station receives a frame that passes the CRC, it waits a short period of time known as the Short Inter-fram Spacing (SIFS) and then sends back an acknowledgment frame. If the transmitting station does not receive an acknowledgment within a given amount of time, it assumes that an error has occurred and retransmits the frame, using the CSMA/CA protocol to access the channel. If an acknowledgment is not received after some fixed number of retransmissions, the transmitting station gives up and discards the frame. Computer Networks R. Wei 37
The outline for CSMA/CA protocol is as follows. Suppose that a station (wireless station or an AP) has a frame to transmit. 1. If initially the station senses the channel idle, it transmits its frame after a short period of time know as the Distributed Inter-frame Space (DIFS). 2. Otherwise, the station chooses a random backoff value using binary exponential backoff (some method to decide the value) and counts down this value when the channel is sensed idle. While the channel is sensed busy, the counter value remains frozen. Computer Networks R. Wei 38
3. When the counter reaches zero (note that this can only occur while the channel is sensed idle), the station transmits the entire frame and then waits for an acknowledgment. 4. If an acknowledgment is received, the transmitting station knows that its frame has been correctly received at the destination station. If the station has another frame to send, it begins the CSMA/CA at step 2. If the acknowledgment is not received, the transmitting station reenters the backoff phase in step 2, with the random value chosen from a larger interval. Computer Networks R. Wei 39
CSMA/CA uses SIFS and random backoff value to hold off the transmission for a short time. The reason is as follows. In the case of wireless LAN, when a station transmits a frame, it does not detect collision. There are some reasons for that. To detect collision, the station requires the ability to send and receive at the same time, which will cost the adapter hardware a lot in the case of wireless. Moreover, in some situation, the station will not be able to detect a collision because of the hidden terminal problem (there are some physical obstacle between two transmitting stations, or it is caused by the fading of the signal strength). Therefore, if two stations find that the channel is in idle and start to transmit, then a collision occur. But if two stations choose different random value of backoff, then the collision can be avoided. Computer Networks R. Wei 40
RTS and CTS Considering the example of hidden terminal in Figure 3. AP H2 H1 Figure 3: Hidden terminal example Computer Networks R. Wei 41
In this example, due to the fading, the signal from H1 cannot reach H2 and the signal from H2 cannot reach H1. So each of the wireless stations is hidden from the other, but neither is hidden from the AP. Suppose station H1 is transmitting a frame and halfway through H1’s transmission, station H2 wants to send a frame to the AP. H2 first wait a DIFS interval and then transmit the frame, resulting a collision (H1 has not finished the transmission). The channel will therefore be wasted during the entire period of H1’s transmission as well as during the H2’s transmission. Computer Networks R. Wei 42
IEEE 802.11 protocol allows a station to use a short Request to Send (RTS) control frame and a short Clear to Send (CTS) control frame to reserve access to the channel. When a sender wants to send a data frame, it can first sent an RTS to the AP, indicating the total time required to send the data frame and the acknowledgment (ACK) frame. When the AP receives the RTS frame, it responds by broadcasting a CTS frame. This CTS frame servers two purpose: it gives the sender explicit permission to send and also instructs the other stations not send for the reserved duration. Computer Networks R. Wei 43
The use of RTS and CTS can improve the performance because: • The hidden station problem is mitigated, since a long data frame is transmitted only after the channel has been reserved. • Because the RTS and CTS frames are short, a collision involving an RTS or CTS frame will last only for the duration of the short RTS or CTS frame. Once the RTS and CTS frames are correctly transmitted, the following data and ACK frames should be transmitted without collisions. Computer Networks R. Wei 44
Although the RTS/CTS exchange can help reduce collisions, it also introduces delay and consumes channel resources. For this reason, the RTS/CTS exchange is only used when the frame is long. In practice, each wireless station can set an RTS threshold such that the RTS/CTS sequence is used only when the frame is longer than the threshold. Computer Networks R. Wei 45
The IEEE 802.11 frame The format of IEEE 802.11 frame is shown as follows: 2 2 6 6 6 2 6 0-2312 4 frame addr addr addr seq addr duration payload CRC control 1 2 3 control 4 Computer Networks R. Wei 46
The numbers above each of the fields in the frame represented the lengths of the field in bytes. The fields are as follows: • Payload: typically consists of an IP datagram of an ARP packet. Usually it is fewer than 1,500 bytes, although this field can be as long as 2,312 bytes. • CRC: a 32-bit cyclic redundancy checksum. Computer Networks R. Wei 47
• Address field: it has four address fields, each of which can hold a 6-byte MAC address. Three address fields are needed for internetworking purpose-specifically, for moving the network-layer datagram from a wireless station through an AP to a router interface. The fourth address field is used when APs forward frames to each other in ad hoc mode. The first three address fields are defined as follows: – Address 2 is the MAC address of the station that transmits the frame. If a wireless station transmits the frame, that station’s MAC address is inserted in the address 2 field. Similarly, if an AP transmits the frame, the AP’s MAC address is inserted to the address 2 field. Computer Networks R. Wei 48
– Address 1 is the MAC address of the wireless station that is to receive the frame. For example, if a mobile wireless station transmits the frame, address 1 contains the MAC address of the destination AP. – To understand address3, recall that the BSS is part of a subnet, and that this subnet connects to other subnets via some router interface. Address 3 contains the MAC address of this router interface. Computer Networks R. Wei 49
• Sequence control: whenever a station correctly receives a frame from another station, it sends back an acknowledgment. If the ACK frame get lost, the sending station may send multiple copies of a given frame. The use of sequence numbers allows the receiver to distinguish between a newly transmitted frame and the retreansmission of a previous frame. • Duration: 802.11 allows a transmitting station to reserve the channel for a period of time that includes the time to transmit its data frame and the time to transmit an acknowledgment. This duration value is included in this field. Computer Networks R. Wei 50
• Frame control: This field includes many subfields including: Protocol version, Type, Subtype, To AP, From AP, More fragment, Retry, Power mgt, More data, WEP, Reserved. The type and subtype fields are used to distinguish the association, RTS, CTS, ACK, and data frame. The to and from fields are used to define the meanings of different address fields. WEP field indicates whether encryption is used. Computer Networks R. Wei 51
Gigabit WiFi Since the speed of Ethernet standard has extended in the gigabit per second range, the speed of WiFi is also requested to extend. IEEE 802.11 has introduced two new standards for that purpose. • IEEE 802.11ac • IEEE 802.11ad Computer Networks R. Wei 52
IEEE 802.11ac operates in the 5 GHz band, same as 802.11a and 802.11n. The new standard achieves much higher data rates than 802.11n by means of enhancements in three areas: • Bandwidth: The maximum bandwidth of 802.11n is 40MHz, but the maximum bandwidth of 802.11ac is 160 MHz. • Signal encoding: 802.11n uses 64 QAM with OFDM, and 802.11ac uses 256 QAM with OFDM. ( Quadrature Amplitude Modulation is a popular analog signaling technique). Thus more bits are encoded per symbol. Both schemes use forward error correction with a code rate of 5/6 (ratio of data bits to total bits). • MIMO: With 802.11n, there can be a maximum of 4 channel input and 4 channel output antennas. 802.11 ac increases this to 8 × 8. Computer Networks R. Wei 53
802.11ac includes the option of multiuser MIMO (MU-MIMO). This means that on the downlink, the transmitter is able to use its antenna resources to transmit multiple frames to different stations, all at the same time and over the same simultaneously spectrum. This enables the AP to deliver significantly more data in many environments. Computer Networks R. Wei 54
IEEE 802.11ad is a version of 802.11 operating in the 60 GHz frequency band. This band offers the potential for much wider channel bandwidth than the 5 GHz band, enabling high data rates with relatively simple signal encoding and antenna characteristics. Few devices operate in the 60 GHz band, which means communications would experience less interference that in the other bands used by 802.11. Computer Networks R. Wei 55
However, at 60 GHz, 802.11ad is operating in the millimeter range, which has some undesirable propagation characteristics: • Since free space loss increases with the square of the frequency, losses are much higher in this range. • Multipath losses can be quite high. • Millimeter wave signals generally don’t penetrate solid objects. For these reasons, 802.11ad is likely to be useful only within a single room. Because it can support high data rates and could easily transmit uncompressed high-definition video, it is suitable for applications such as replacing wires in a home entertainment system, of streaming high-definition movies from your cell phone to your television. Computer Networks R. Wei 56
Whereas 802.11ac supports a MIMO antenna configuration, 802.11ad is designed for single antenna operation. And 802.11ad has a huge channel bandwidth of 2160 MHz. Computer Networks R. Wei 57
5.3 Bluetooth Bluetooth is a wireless technology that uses short-range digital radio communications and offers fast and reliable transmission of both voice and data. Bluetooth is defined in the IEEE 802.15.1 standard. Now Bluetooth is managed by the Bluetooth Special Interest Group (SIG), which has more than 25,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. The IEEE no longer maintains the standard. The Bluetooth SIG oversees development of the specification, manages the qualification program, and protects the trademarks. Computer Networks R. Wei 58
It is essentially a low-power, short-range, low-rate “cable replacement” technology for interconnection devices. Bluetooth incorporates a radio frequency transceiver and a full set of networking protocols on a single chip that is small enough to be included in cellular and cordless phone, portable PCs, headsets, etc. Sometimes, 802.15.1 networks are referred as wireless personal area networks (WPANs). Computer Networks R. Wei 59
802.15.1 networks operate in the 2.4GHz unlicensed radio band in a TDM manner, with time slots of 625 microseconds. During each time slot, a sender transmits on one of 79 channels, with the channel changing in a known but pseudo random manner from slot to slot. This form of channel hopping, known as frequency-hopping spread spectrum (FHSS), spreads transmissions in time over the frequency spectrum. It can provide data rate up to 4 Mbps. Computer Networks R. Wei 60
Some layers and protocols of Bluetooth. • Bluetooth Radio layer: This is the lowest defined layer of the bluetooth specification. It is not a protocol, but defines the requirements and operations of the bluetooth transceiver device, transmitting and receiving radio frequency signals in the 2.4GHz ISM band. • Baseband: This is the physical layer protocol of the bluetooth specification and it lies on top of the bluetooth radio layer. • Link Manager Protocol(LMP): LMP performs the link setup, configuration and authentication process within the bluetooth stack. After the Link Manager(LM) of one device discovers the LM of another device, the LMP then communicates with the remote LM to establish a link. Computer Networks R. Wei 61
• Host Controller Interface (HCI): HCI provides a commend interface between the baseband control and the LM. • L2CAP (Logical link control and adaptation protocol): The L2CAP resides on data-link layer (OSI model) and provides the link functions for the baseband protocol. • RFCOMM (Radio frequency communication): is the cable replacement protocol in the bluetooth stack. It creates a virtual seral port through which RF communications can be passed using standard EIA/TIA (Electronics Industries Association/Telecommunications Industry Association) 232 standard, which is the serial port communication standard. Computer Networks R. Wei 62
• Object Exchange Protocol (OBEX): Originally specified by the Infrared Data Association (IrDA), OBEX is used to transfer data, graphics and voice objects between devices. OBEX is used in serval devices, such as PDAs (personal digital assistants), mobile phones and computer systems. • vCard/vcal: A protocol used to store and transfer virtual business cards and personal calenders on mobile devices. • TCP (Telephony control protocol): Used to set up and control speech and data calls between Bluetooth devices. The protocol is based on the ITU-T standard Q.931, with the provisions of Annex D applied, making only the minimum changes necessary for Bluetooth. TCP is used by the intercom (ICP) and cordless telephony (CTP) profiles. Computer Networks R. Wei 63
• AT command set: It includes the control commands used to control dial-up modem functions and actions. • Telephone Control Specification–Binary(TCS BIN): It is a bit-oriented protocol used to establish voice and data links between bluetooth devices. • Service Discovery Protocol (SDP): Bluetooth requires an SDP to identify and manage the services available on portable devices moving into and out of range with each other. The Bluetooth SDP is specifically designed for bluetooth devices. Computer Networks R. Wei 64
• Synchronous connection-oriented (SCO)link: The type of radio link used for voice data. An SCO link is a set of reserved timeslots on an existing ACL (Asynchronous Connection-Less) link. Each device transmits encoded voice data in the reserved timeslot. There are no retransmissions, but forward error correction can be optionally applied. SCO packets may be sent every 1, 2 or 3 timeslots. Enhanced SCO (eSCO) links allow greater flexibility in setting up links: they may use retransmissions to achieve reliability, allow a wider variety of packet types, and greater intervals between packets than SCO, thus increasing radio availability for other link. Computer Networks R. Wei 65
In bluetooth, communications are between wireless stations (no APs). The operation of bluetooth networks (called piconets) is based on the master-slave principle, where one station is the master and other stations (up to 7) become the slaves. Bluetooth technology can also provide a link to a wired network in a similar way that 802.11 access point do, by installing a bluetooth access point that is connected to a wired network. An ad-hoc bluetooth network piconet can include up to 8 bluetooth devices. When more than 8 device are attempting to associate with a piconet, the piconet is divided into two or more piconets, and then interconnected into what is called a scatternet. Computer Networks R. Wei 66
A bluetooth device cannot act as a master for two piconet. If a piconet master device is also linked to another piconet in a scatternet, it must participate as a master device in one piconet and a slave device in a second piconet. The slaves that share the same master device belong to the same pibonet and to remain as a member of a piconet, each slave must interact with the master on a time interval negotiated between the master and the salve. If the master leaves the piconet, the other devices must elect a new master and the piconet is reformed. When a bluetooth device is a member of two piconets, it can be used as a link between the piconets. Computer Networks R. Wei 67
Any bluetooth device is capable of serving as a master or a slave, depending on the networking situation it encounters on-the-fly. A piconet can be formed using one of the following methods: • A master device actively scans for slave devices and, when it detects one in its range, it can invite the device to join a piconet as a slave. • A master device can passively wait for a slave to contact it, and then invite the slave to join the piconet as a slave. Computer Networks R. Wei 68
Bluetooth devices each have a unique clock signal and device address, which are combined to provide a unique identity. The difference or offset between one device’s clock signal and the clock signal of another device is the basis for the FHSS (frequency-hopping spread-spectrum) sequence used between the devices to transmit data. Computer Networks R. Wei 69
Bluetooth device use frequency hopping in order to avoid interference with other devices that operate in the same unlicensed ISM (Industrial Scientific and Medical) band. The frequency-hopping scheme uses 79 different channels and changes frequency 1600 times per second in a pseudo-random matter. This makes eavesdropping slightly more difficult. Bluetooth is a short range radio technology enabling communications over a few meters only (mostly in class 2 that is for 10 meters). That means that an attacker must be physically close to the victims in order to eavesdrop the communications, which also reduces the likelihood of attacks. Computer Networks R. Wei 70
5.4 Mobility management Now we consider the situation about a mobile user how to maintain ongoing connections while moving between notworks. In the case of mobile, the mobile node (such as a smartphone or a laptop) needs a “permanent home address” known as home network, and an entity within the home network that performs the mobility management functions on behalf of the mobile node known as the home agent. The network in which the mobile node is currently residing is known as the foreign (or visited) network, and the entity within in the foreign network that helps the mobile node with the mobility management functions is known as a foreign agent. A correspondent is the entity wishing to communicate with the mobile node. Computer Networks R. Wei 71
Mobile IP One role of the foreign agent is to create a so called care-of address (COA) for the mobile node, with the network portion of the COA matching that of the foreign network. So there are two addresses associated with a mobile node, its permanent address and its COA, sometimes known as a foreign address. Although we have separated the functionality of the mobile node and the foreign agent, it is worth to note that the mobile node can also assume the responsibility of the foreign agent. Computer Networks R. Wei 72
The Internet architecture and protocols for supporting mobility, collectively known as mobile IP, are defined primarily in RFC 5944 for IPv4. Mobile IP is a flexible standard, supporting many different modes of operation, multiple ways for agents and mobile nodes to discover each other, use of single or multiple COAs, and multiple forms of encapsulation. Computer Networks R. Wei 73
The mobile IP standard consists of three main pieces: • Agent discovery. • Registration with the home agent. • Indirect routing of datagrams. Computer Networks R. Wei 74
Agent discovery Agent discovery can be accomplished in one of two ways: via agent advertisement or via agent solicitation. With agent advertisement, a foreign or home agent advertises its services using an extension to the existing router discovery protocol. The agent periodically broadcast an ICMP message with a type of 9 (router discovery) on all links to which it is connected. The router discovery message contains the IP address of the router (the agent), thus allowing a mobile node to learn the agent’s IP address. Computer Networks R. Wei 75
The router discovery message also contains a mobility agent advertisement extension that contains additional information needed by the mobile node. The format of the ICMP router discovery message with mobility agent advertisement extension is as in Figure 4. Computer Networks R. Wei 76
0 8 16 27 Type = 9 Code = 0 Checksum Router address Type = 16 Length Sequence number Registration lifetime RBHFMGrTUXI Reserved 0 or more care-of addresses . . . Figure 4: Discovery message Computer Networks R. Wei 77
In Figure 4, the upper part contains the standard ICMP fields and the lower part is the mobility agent advertisement extension. Some of the fields are explained below. • Registration required bit (R): Registration with this foreign agent (or another foreign agent on this link) is required even when using a co-located care-of address. • Busy bit (B): The foreign agent will not accept registrations from additional mobile nodes. • Home agent bit (H): Indicates that the agent is a home agent for the network in which it resides. • Foreign agent bit (F): Indicates that the agent is a foreign agent for the network in which it resides. Computer Networks R. Wei 78
• Registration required bit (R): Indicates that a mobile user in this network must register with a foreign agent. In particular, a mobile user cannot obtain a care-of address in the foreign network (for example, using DHCP) and assume the functionality of the foreign agent for itself, without registering with the foreign agent. • M, G encapsulation bits: Indicate whether a form of encapsulation other than IP-in-IP encapsulation will be used. • Care-of address fields: A list of one or more care-of addresses provided by the foreign agent. Computer Networks R. Wei 79
For agent solicitation, a mobile node wanting to learn about agents without waiting to receive an agent advertisement can broadcast an agent solicitation message, which is simply an ICMP message with type value 10. An agent receiving the solicitation will unicast an agent advertisement directly to the mobile node, which can then proceed as if it had received an unsolicited advertisement. Computer Networks R. Wei 80
Registration with the home agent Once a mobile IP node received a COA, that address must be registered with the home agent. This can be done either via the foreign agent (who then registers the COA with the home agent) or directly by the mobile IP node itself. Computer Networks R. Wei 81
Registering by the foreign agent is as follows. 1. By receipting a foreign agent advertisement, a mobile node sends a mobile IP registration message to the foreign agent. The registration message is carried within a UDP datagram and sent to port 434. The registration message carries a COA advertised by the foreign agent, the address of the home agent (HA), the permanent address of the mobile node (MA), the requested lifetime of the registration, and a 64-bit registration identification. The registration identifier acts like a sequence number and serves to match a received registration reply with a registration request. Computer Networks R. Wei 82
2. The foreign agent receives the registration message and records the mobile node’s permanent IP address. The foreign agent now knows that it should be looking for datagram containing an encapsulated datagram whose destination address matches the permanent address of the mobile node. The foreign agent then sends a mobile IP registration message to port 434 of the home agent. The message contains the COA, HA, MA, encapsulation format requested requested registration lifetime, and registration identification. Computer Networks R. Wei 83
3. The home agent receives the registration request and checks for authenticity and correctness. The home agent binds the mobile node’s permanent IP address with the COA. The home agent sends a mobile IP registration reply containing the HA, MA, actual registration lifetime, and the registration identification of the request that is being satisfied with this reply. 4. The foreign agent receives the registration reply and then forwards it to the mobile node. Computer Networks R. Wei 84
Indirect routing of datagrams The mobile node informs its home agent of its current location using the registration procedure described above. Home agents and foreign agents will support tunneling datagrams using IP-in-IP encapsulation. Any mobile node that uses a care-of address will support receiving datagrams tunneled using IP-in-IP encapsulation. Computer Networks R. Wei 85
When connected to its home network, a mobile node operates without the support of mobility services. That is, it operates in the same way as any other (fixed) host or router. ICMP Router Advertisement is one such method as we discussed before. Computer Networks R. Wei 86
When registered on a foreign network, the mobile node chooses a default router. Upon receipt of an encapsulated datagram sent to its advertised care- of address, a foreign agent compares the inner Destination Address to those entries in its visitor list. When the Destination does not match the address of any mobile node currently in the visitor list, the foreign agent will not forward the datagram. Otherwise, the foreign agent forwards the decapsulated datagram to the mobile node. Computer Networks R. Wei 87
The home agent is able to intercept any datagrams on the home network addressed to the mobile node while the mobile node is registered away from home. The home agent must examine the IP Destination Address of all arriving datagrams to see if it is equal to the home address of any of its mobile nodes registered away from home. If so, the home agent tunnels the datagram to the mobile node’s currently registered care- of address or addresses. Computer Networks R. Wei 88
The mobile IP standard allows many additinal scenarios and capabilities in addition to the above description. RFC 5944 contains more than 100 pages. Mobile IPv6 is defined in RFC 6275, which we omit here. Computer Networks R. Wei 89
5.5 Mobile Sensor Networks Wireless sensor networks (WSN) usually integrate a large number of low-power, low-cost sensor nodes. They are largely deployed to monitor a specific environment. There are many different applications of WSNs: • Military applications: Wireless sensor networks be likely an integral part of military command, control, communications, computing, intelligence, battlefield surveillance, reconnaissance and targeting systems. • Area monitoring: In area monitoring, the sensor nodes are deployed over a region where some phenomenon is to be monitored. When the sensors detect the event being monitored (heat, pressure etc), the event is reported to one of the base stations, which then takes appropriate action. Computer Networks R. Wei 90
• Transportation: Real-time traffic information is being collected by WSNs to later feed transportation models and alert drivers of congestion and traffic problems. • Health applications: Some of the health applications for sensor networks are supporting interfaces for the disabled, integrated patient monitoring, diagnostics, and drug administration in hospitals, tele-monitoring of human physiological data, and tracking and monitoring doctors or patients inside a hospital. • Environmental sensing: The term Environmental Sensor Networks has developed to cover many applications of WSNs to earth science research. This includes sensing volcanoes, oceans, glaciers, forests etc. Computer Networks R. Wei 91
• Structural monitoring: Wireless sensors can be utilized to monitor the movement within buildings and infrastructure such as bridges, flyovers, embankments, tunnels etc enabling Engineering practices to monitor assets remotely with out the need for costly site visits. • Industrial monitoring: Wireless sensor networks have been developed for machinery condition-based maintenance (CBM) as they offer significant cost savings and enable new functionality. In wired systems, the installation of enough sensors is often limited by the cost of wiring. • Agricultural sector: using a wireless network frees the farmer from the maintenance of wiring in a difficult environment. Irrigation automation enables more efficient water use and reduces waste. Computer Networks R. Wei 92
Sensor networks often have one or more points of centralized control called base stations. sensor nodes are small in size and able to sense, process data and communicate with each other, typically over an RF (radio frequency) channel. In general, there are three categories of traffic: • Many-to-one traffic. • One-to-many traffic. • Local traffic: The nodes in a limited area send localized messages to discover the neighbouring nodes and coordinate with each other. May be broadcast or send messages intended for a single neighbour. Computer Networks R. Wei 93
WSN Features The basic features of WSNs: • Self-organizing capabilities. The WSNs are able to cope with topology variability and infrastructure variations. • Short-range broadcast communication and multirouting. The sensor nodes have reduced radio ranges and should cooperate to achieve complete routing of information. • Dense deployment and cooperative effort of sensor nodes. The shortage of the radio range and the need to have efficient sensing call for a dense deployment of sensors. • Limitations of energy, transmit power, memory and computing power. WSNs cope with limitation of resources and frequent changes of topology due to fading and node failures. Computer Networks R. Wei 94
Some of the challenges for WSNs: • Extension of lifetime. A typical alkaline battery, for example, provides about 50 watt-hours of energy. Given the expense and the potential infeasibility of monitoring and replacement of batteries for a large WSN, significantly longer lifetimes would be desired. • Responsiveness. A simple solution to extending network lifetime is to operate the nodes in a duty-cycled manner with periodic switching between sleep and wake-up modes. This causes the time synchronizing requirement, and the responsiveness of and the effectiveness of the sensors. Computer Networks R. Wei 95
• Robustness. The use of large number of inexpensive devices characterizes the WSNs. It is important to ensure that the global performance of the system is not sensitive to individual device failure. It is also often desirable that the performance of the system degrade as gracefully as possible with respect to component failure. • Synergy. Design synergistic protocol, which ensures that the system as a whole is more capable than the sum of the capabilities of its individual component. The protocols must provide an efficient collaborative use of storage, computation and communication resources. Computer Networks R. Wei 96
• Self-configuration. WSNs are inherently unattended distributed systems. Autonomous operation of the network is therefore a key design. Nodes in a wireless sensor network have to be able to configure their own network topology, synchronize, and calibrate themselves; coordinate inter-node communication; and determine other important operating parameters. • Privacy and security. The large scale, prevalence, and sensitivity of the information collected by WSN (as well as their potential deployment in hostile locations) give rise to the final key challenge of ensuring both privacy and security. Computer Networks R. Wei 97
Structure of WSN Structure of a Wireless Sensor Network includes different topologies for radio communications networks. • Star network (single point-to-multipoint): A star network is a communications topology where a single base station can send and/or receive a message to a number of remote nodes. The remote nodes are not permitted to send messages to each other. The advantage of this type of network for wireless sensor networks includes simplicity, ability to keep the remote node’s power consumption to a minimum. It also allows low latency communications between the remote node and the base station. The disadvantage of such a network is that the base station must be within radio transmission range of all the individual nodes and is not as robust as other networks due to its dependency on a single node to manage the network. Computer Networks R. Wei 98
• Mesh network: A mesh network allows transmitting data to one node to other node in the network that is within its radio transmission range. This allows for what is known as multi-hop communications. This network topology has the advantage of redundancy and scalability. If an individual node fails, a remote node still can communicate to any other node in its range, which in turn, can forward the message to the desired location. In addition, the range of the network is not necessarily limited by the range in between single nodes; it can simply be extended by adding more nodes to the system. The disadvantage of this type of network is in power consumption for the nodes that implement the multi-hop communications are generally higher than for the nodes that dont have this capability, often limiting the battery life. Additionally, as the number of communication hops to a destination increases, the time to deliver the message also increases. Computer Networks R. Wei 99
• Hybrid star–Mesh network: A hybrid between the star and mesh network provides a robust and versatile communications network, while maintaining the ability to keep the wireless sensor nodes power consumption to a minimum. In this network topology, the sensor nodes with lowest power are not enabled with the ability to forward messages. This allows for minimal power consumption to be maintained. However, other nodes on the network are enabled with multi-hop capability, allowing them to forward messages from the low power nodes to other nodes on the network. Generally, the nodes with the multi-hop capability are higher power, and if possible, are often plugged into the electrical mains line. This is the topology implemented by the up and coming mesh networking standard known as ZigBee. Computer Networks R. Wei 100
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